1. Field of the Invention
The invention relates generally to the field of expansion of particulate material capable of expansion by rapid internal decompression without substantial disintegration. More particularly, it relates to expansion of grain or cattle fodder, wherein grain or fodder is heated, steamed and pressurized and is then ejected into a lower pressure region where it rapidly decompresses into a much expanded form, whereby physical and chemical properties are beneficially altered.
2. Description of Prior Art
Various processes and apparatus have been developed over the past few decades for modifying or converting cereal grain into a form more readily consumable by humans, typically into some form of breakfast food. These include processes for converting cereal grain into a flake form, like corn flakes, by steaming and then rolling or flaking it, or into a puffed form, like puffed wheat, by steam pressurizing the grain and then ejecting it into a lower pressure region where it explosively decompresses into a much expanded form (for example, U.S. Pat. Nos. 2,622,985; 2,698,799 and 2,838,401 for puffing cereal grains). Still other processes employ pressure cooking to partially or fully cook starchy grains such as rice (for example, U.S. Pat. Nos. 2,525,137; 2,758,031; 3,085,011 and 3,085,013).
More recently, attempts have been made to adapt such processes to treating fodder material for cattle (the term cattle as used herein also includes other types of livestock and the term fodder as used herein includes various types of grain). The principal objective is to reduce feed costs, particularly at large feed lots, by creating an altered or modified fodder from which cattle can extract more nourishment. It appears this can be accomplished by irreversibly breaking down the large molecules of relatively hard to digest starch in the fodder into smaller molecules of more easily digested dextrin.
Initially the fodder treatments involved either pressure cooking the fodder or steaming and then rolling or flaking it. However, the maximum benefit sought was not achieved because the conversion of starch into dextrin by these processes is largely reversible. As a consequence, at least some of the dextrin reconverts to starch before the animal's digestive process begins.
In 1972, Algeo (U.S. Pat. No. 3,667,961) described a batch process for irreversibly breaking down the starch in fodder materials into dextrin. This process, similar to those used for puffing cereal grains, included pressurizing the fodder in a steam atmosphere at moderately high temperatures for a short period of time before ejecting it into the atmosphere where the pressurized particles explosively depressurized into a much expanded form. In theory, the steaming softens the fodder particles and allows them to become internally pressurized, and the subsequent explosive depressurization physically ruptures chemical bonds in the starch molecules, thereby irreversibly breaking down the starch molecules into dextrin molecules. Algeo described several side benefits including (1) increased porosity of the expanded fodder which allows easy penetration of the livestock's digestive juices, (2) thermal decomposition into harmless form of most chemical pesticides which may have been used on the fodder, and (3) destruction of any weed seed in the fodder, thereby providing for a weed-free manure.
This fodder expansion process appears to have achieved promising results in small scale practice and was given wide publicity, a feed cost reduction of from six to nine dollars per head of cattle being then estimated. (The estimated savings per head is currently about nineteen dollars.) However, for numerous reasons to be examined, the results in actual use have not lived up to expectations.
The principal use of fodder expanders is at centralized feed lots where large numbers of cattle are gathered to be fattened for market. These feed lots contain tens or hundreds of thousands of cattle which consume vast quantities of fodder (approximately 24 pounds per head of cattle per day). Location of the fodder expansion apparatus in the immediate vicinity of the feed lots is essential to avoid the prohibitive cost of shipping such quantities of bulky expanded fodder. The apparatus must thus be used in a field, as opposed to a laboratory or factory, environment and is located in relatively remote regions where equipment servicing is expensive and inconvenient and where well trained operating and maintenance personnel are unlikely to be found. Another economic feasibility requirement is that the expansion apparatus must be in substantially continuous operation to meet the fodder demands. It must therefore be extremely reliable.
Fodder expansion apparatus heretofore used have, to the contrary, proven quite unreliable. A major reason for this unreliability relates to the fact that satisfactory means has not previously, to the applicant's knowledge, been developed for introducing the untreated fodder into the pre-expansion pressurizing region without first depressurizing the region; that is, only batch expanders have as yet been employed. In a batch expander, the pressure vessel in which the fodder is heated and pressurized is first filled with fodder and then pressurized with steam. After a short pressurization period, the fodder is ejected to the atmosphere for expansion. The vessel must be vented before another batch of fodder is introduced and then repressurized before processing of the new batch is commenced. To compensate for lost vessel-filling time in order to achieve reasonable flow rates of fodder through the apparatus, the pressurization period is generally made quite short -- typically only about 15 to 20 seconds -- representing only a fraction of the entire batch cycling time. This short pressurization period, because of the relatively large, stationary mass of fodder, generally results in inadequate pressurization of a significant amount of the fodder, with the result that these under-pressurized particles do not subsequently expand sufficiently to convert all the starch to dextrin. To further compensate for lost vessel-filling time, fodder particles are generally transported through the apparatus at high velocity. Because of the abrasiveness of the fodder, rapid internal wear of the apparatus, particularly in regions (such as elbows) of abrupt direction change, results and frequent shutdowns are necessary to replace eroded parts.
Still other problems relate to the general use of large quantities of high quality, that is, dry, boiler steam for heating and pressurizing the fodder and for ejecting it to the atmosphere. Further, the cyclic venting of the pressurized vessel causes moderate losses of high energy steam and is therefore wasteful not only of the boiler feed water from which the steam is created, but also of the energy used to create the steam. This large consumption of boiler steam by existing equipment has necessitated installation at feed lots of extensive water softening facilities for producing boiler feed water. This not only results in added expense, but problems associated with the water softening systems have frequently caused shutdown of the entire expansion apparatus.
Another major problem has been that the expanded fodder generally requires auxiliary drying before handling or storage because of its high water content. This is because the moisture initially present in the fodder -- typically twelve to fifteen percent by weight -- operates as an energy sink and absorbs so much energy from the pressurizing and the ejecting steam that some of the steam is condensed into water. When this water is ejected with the fodder, it is absorbed by the expanded fodder, causing the expanded fodder to be too wet to be easily handled or stored. In order to produce, by present expansion processes and apparatus, an expanded fodder sufficiently dry for handling or storage, steam boiler horsepower would have to be increased several fold. Generally, as an alternative to increasing boiler horsepower, large auxiliary dryers are used to dry the expanded fodder, thereby still greatly increasing system complexity and cost.
A problem of increasing significance is the high noise level produced by the expansion process. The explosive decompression of the material is not the sole noise source. Considerable noise is produced by supersonic expansion of the high pressure steam leaving the ejection opening or nozzle. When the ejection region is full of fodder, the steam expansion noise is attenuated to some extent; however, in batch processing there are frequent periods when there is an outflow of expanding steam with the ejection region virtually empty of fodder, and thus there is no noise attenuation. Also, no attention has previously been directed to the fact that the nozzles or restrictive openings used at the ejection point have subsonic characteristics, whereas the steam expansion is generally supersonic.
An object of this invention is to provide an improved apparatus for expanding fodder material whereby the desired beneficial results may be achieved with minimized deficiencies such as above described. To this end, a continuous flow fodder expander is provided which recirculates boiler steam to create heating, pressurizing and ejecting steam from untreated city water and which automatically maintains a predetermined ejection region enthalpy regardless of moisture content of the fodder, in order to insure a dry expanded product.
The system to be described, with relatively low fuel flow and without requiring superheat, obtains a consistent lightweight product having low moisture content. It can handle different grains on an individual basis and is capable of processing high bulk density products that are resistant to flow. The system is more efficient than known steam processes in that it processes more grain for the same system input energy or can produce higher nozzle enthalpy with the same product weight per unit of time. The system is automatically controlled to handle the particular product and is also adjustable to handle different products of different bulk density.
Other objects will be apparent from the description and the appended claims.